This research investigates the behavioral and pharmacological means through which rat mothers calm their infants and induce antinociception. Two classes of maternal stimuli, gustatory and tactile, have these properties and influence infant state through two different mechanisms: opioid and nonopioid respectively. Specific Aim I is an intensive behavioral and pharmacological analysis of the properties of the nonopioid system in Day 10 rats focusing pharmacologically on the antinociception. It seeks to identify the portion of the GI tract through which different calming and antinociceptive agents achieve their effect. This will feature infusing effective substances into the mouth, or stomach, and evaluating the effects of infusions on heat-withdrawal latency and reduction of isolation distress vocalizations. Changes in these behaviors, should they occur, will be reversed by intraperitoneal injections of different opioid antagonists. The second goal of Specific Aim II is to determine whether milk is working indirectly through the release of endogenous cholecystokinin (CCK). The calming effect of milk will be tested against MK-329, and L365,260 peripheral and central CCK antagonists, respectively. Specific Aim III seeks to extend the findings obtained in Day 10 rats to older infants, especially those of weaning age, in an effort to identify the bases of change in reaction to the dam by the infant. This entails replicating the major experimental findings in Aims I-II in 16-, 22-, and 28-day-old-rats. Specific Aim IV assess the longer term consequences of particular maternal influences by evaluating reactions to an odor paired with either tactile or gustatory maternal stimulation. Alterations in odor preference, in levels of vocalization during isolation and in pain threshold will be determined in the presence of the associated odor. The mechanisms underlying preference formation will be determined by selective blockade of opioid and 5-HT systems during conditioning; mechanisms underlying performance will be similarly assessed during testing. This proposal is of developmental interest because it will reveal some of the mechanisms through which mothers influence their young and how these fundamental influences change over time. They will also reveal potential lasting effects of these influences beyond their proximal effects. They will provide a basis for evaluating normal development and that of infants from abnormal populations (drug addiction, for example).